The present disclosure relates generally to centrifugal submersible pumps and, more particularly, to assemblies and methods for pumping fluids containing solids.
Frequently, an underground pump is used to force fluids toward the surface. An electric submersible pump (ESP) may be installed in a lower portion of the wellbore. There are several problems connected with the downhole pumping of fluid containing solids, such as coal fines or scale from a source such as a coal field or other energy liquid sources. These problems generally result in premature failure of the submerged pump.
One problem is the presence of large coal or other solids particles which flow through the pump and cause damage thereto. Another problem is excessive wear, e.g., in a water-coal slurry environment) due to low fluid velocity resulting from low intake pressure or high solids-to-fluid ratios. Lower volumes and low velocity create areas of pressure drop that allow the solids to drop out and become lodged in the low pressure areas of the pump stage. Compounding that problem is that, with build-up of solids through often tortuous flowways of conventional pumps, the increasing build-up may eventually prohibit the pump from producing fluid.
Yet another problem is vapor lock which occurs when the flow of water is too low compared with the amount of gas present. In wells with high volumes of gas, gas separators may also be included, to separate gas from the rest of the produced fluids. The gas may be separated in a mechanical or static separator and vented to the annulus. The remainder of the produced fluid may enter the ESP, which may pump it to the surface via production tubing. In wells producing gas, the ESP may be used to pump water out of the wellbore to maintain the flow of unconventional gas, which may include methane gas, for example. In this instance, the water is pumped up production tubing, while the methane gas flows up the annulus between the production tubing and the wellbore. However, some methane gas entrained in the water will be pumped by the pump. Wells that are particularly “gassy” may experience a significant amount of the methane gas passing through the pump, which may cause gas lock, resulting in costly and time-consuming shutdowns.